1. Field of the Invention
This invention relates to a tapping screw, particularly to one possible to force cut wood waste move out of an object being fixed, and to shorten a cutting member as possible, and to elevate fixing force of a screw.
2. Description of the Prior Art
A first conventional tapping screw 1 shown in FIGS. 1 and 2, includes a head 10, a shank 11 provided with male threads 110, a cutting member 12 provided with a plurality of cutting grooves 120 and a plurality of wings 121 projecting outward from the outer surface of the cutting member 12. The wings 121 are formed in parallel vertically to the cutting grooves 120 so that the cutting member may be formed with one round of process. The wings 121 respectively have an inclined cut surface 1210 respectively formed at its lower side.
A second conventional tapping screw 2 shown in FIG. 3 includes a head 20, a shank 21, and cutting member 22. The cutting member 22 has a plurality of cutting grooves 220 vertically formed, and a plurality of wings 221, but the wings 221 are not parallel to the cutting grooves 220, so the cutting grooves 220 and the wings 221 needs a separate process, that is, two processes for forming, resulting in high cost.
A third conventional tapping screw shown in FIG. 4 includes also a head, a shank, and a cutting member 32, which is especially elongate, forming a plurality of cutting grooves 320 elongate for containing cut wood waste therein.
The common disadvantage of the three kinds of conventional tapping screw mentioned above is that the cutting grooves are located in the lower end portion of a screw, regardless of the cutting grooves being long or short. Then in drilling and fixing a screw on an object as shown in FIG. 5, wood waste 41 coming from a drilled hole 40 moves upward along the cutting grooves 13, 23 or 33 as shown respectively in FIGS. 1, 3 and 4, exhausted out of the opening 400 of the drilled hole 40. Then wood waste in the cutting grooves may gradually be piled more and more in accordance with the space of the cutting grooves becoming smaller and smaller (the upper portion becomes smaller the lower portion), due to the wood waste continually produced. The sharpness of the outer edges of the cutting grooves and the pointed ends decreases gradually, blocked by the wood waste therein so that the screw may be impossible to pass through an object such as a steel plate 42.
As seen in FIGS. 1 and 4, the conventional tapping screw have the wings 121, 221 321 provided with the inclined surfaces 1210, 2210, 3210, which may function to cut the drilled hole 420 of a steel plate to a larger hole to form a trumpet-like hole 421. Then only a small portion instead of the whole portion of the male threads can engage with the hole 420, resulting in insufficient force of fixing of the screw with an object.